Folding down the backrest onto the seat especially enables objects larger than the boot of the vehicle to be loaded into the boot. We already know of fully or partially folding backrests such as the backrests usually called "1/3-2/3".
Generally speaking, such locking devices must ensure automatic locking when the backrest is raised; unlocking being achieved by control means such as a push button.
Known locking systems include a hook attached to the car body inside the boot and a movable elastic recall locking element, installed on the backrest, which latch onto the hook when the backrest is raised. An unlocking control element, for example a button, also installed on the backrest, enables the locking element to be disengaged from the hook to unlock the backrest.
A locking system such as this is notably described in document FR-A-2 720 985, the hook penetrates, when the backrest is raised, into a window in the rear wall of the backrest, and the locking element consists of a wire ring, elastically deformable, placed behind this window and onto which the hook latches to ensure locking.
For current use of a vehicle equipped with a rear seat with a folding backrest, the backrest must be correctly locked to prevent it from inadvertently folding down and placing the user in danger subsequent to the intrusion of luggage into the vehicle's passenger compartment. It is therefore advisable to be able to easily ensure that the backrest is effectively locked.
For the system described in the above mentioned document, the unlocking button is connected to the ring and stands proud of the backrest when the ring is not deformed, that is in unlocked position, when the hook is not inserted in the window. When the hook starts to engage in the window in the backrest, it pushes back the locking element and retracts the button which is connected to it inside the well guiding this button, until the hook reaches the locking position where the locking element returns elastically into a slot in the hook. The various elements are sized so that in this locking position, the button does not stand proud of the backrest.
However, in the intermediary position, where the hook pushes back the locking element and before it returns to locked position, the button is also no longer visible. Thus, the fact that the button is visible indicates that locking is not effective, but, conversely the fact that the button is not visible does not guarantee that locking has been correctly achieved. The indication given by the fact that this button is visible or not is not therefore sufficiently reliable.
A similar problem exists in all cases where the unlocking control element is not connected to the locking element and returns elastically into position when released, as the position of this control element is the same whether locking is effective or not.
Other locking systems are known which generally include an unlocking button acting on a movable locking element to place the latter in an unlocked position. These buttons are conventionally accessible from the inside of the passenger compartment of the vehicle. The result is that, even if the boot cannot be opened from the outside, it is accessible to a person who has entered the passenger compartment.